The longer the extension the better for the most part. Nuts/Bolts are 1/2" or 15mm(I think), but I know for sure 1/2" will work, although I usually use a metric size. Swivels are good, and will work for most of them, but one nut on the right side is VERY difficult to get with a swivel...universal joints work better on that one if you can loosen them by hand, as you cant use an impact with a universal joint.
O2's are 7/8". I like to use a very long flat head screw driver for disconnecting the O2 harness connectoer.